As a transmission apparatus for a vehicle, generally referred to as a transaxle, which incorporates a final reduction gear unit in a casing thereof, there are two types such as a transverse-type transmission apparatus and a longitudinal-type transmission apparatus. The transverse-type transmission apparatus incorporates the final reduction gear unit parallel to an axis line direction of the transmission apparatus, and the longitudinal-type transmission apparatus incorporates the final reduction gear unit at an end portion in the axis line direction of the transmission apparatus. Illustrated in FIGS. 7-9 is an example of a conventional longitudinal-type transmission apparatus. A casing 101 includes a transmission case 103 and a final reduction gear unit case 102. The transmission case 103 houses, therein, shift gear shafts such as an input shaft 120 and an intermediate shaft 121 arranged in parallel to each other, and drive side shift gears (hereinafter, referred to as drive gears) 122a-127a and driven side shift gears (hereinafter, referred to as driven gears) 122b-127b. The drive gears 122a-127a are respectively mounted on the shift gear shaft 120, while the driven gears 122b-127b are respectively mounted on the intermediate gears 121, which all are selectively operated by selector sleeves 128-130. The final reduction gear unit case 102 is provided at an end portion in an axis line direction of the transmission case 103 for housing, therein, a final reduction gear unit 135. According to the example illustrated in FIGS. 7-9, the transmission case 103 includes a middle part case 103a and a front part case 103b. The final reduction gear unit case 102, the middle part case 103a, and the front part case 103b are integrally connected to one another in such a manner that the middle part case 103a is interposed between the final reduction gear unit case 102 and the front part case 103b. 
A first end portion of the shift gear shaft 120 is supported, through a rolling bearing, at an end wall 103k of the front part case 103b, and a second end portion of the shift gear shaft 120 is supported, through a rolling bearing, at a boss portion 102e formed on a dividing wall 102a of the final reduction gear unit case 102. A first end portion of the intermediate shaft 121 is supported, through a rolling bearing, at the end wall 103k of the front part case 103b, and a second end portion of the intermediate shaft 121 is supported, through a rolling bearing, at a boss portion 102d formed on the dividing wall 102a of the final reduction gear unit case 102. Further, middle portion of the shift gear shafts 120 and 121 are supported, through rolling bearings, at a transmission chamber dividing wall 103c of the middle part case 103a. The casing 101 includes a final reduction chamber 101A in the final reduction gear unit case 102, and includes a transmission chamber 101B between the dividing wall 102a of the final reduction gear unit case 102 and the transmission case 103. The transmission chamber 100B is divided into a middle part transmission chamber 101B1 and a front part transmission chamber 101B2 by means of the transmission chamber dividing wall 103c. The shift gears 126a, 127a, 126b, and 127b and the selector sleeve 130 are placed in the middle part transmission chamber 101B1, and the shift gears 122a-125a and 122b-125b and the selector sleeves 28 and 29 are placed in the front part transmission chamber 101B. As illustrated in FIGS. 7 and 9, a first oil pool 114 shaped as a half circular arc is provided at a lower part of the middle part transmission chamber 101B1 and covers a lower side of the shift gears 126b and 127b by leaving some space. The first oil pool 114 is supported with its first end fixed to a half circular arc shaped flange portion 103d, which protrudes toward an inside of the middle part transmission chamber 101B1, and its second end fixed to an end surface of the final reduction gear unit case 102. A second oil pool 115, being a half circular arc, is provided at a lower part of the front part transmission chamber 101B2 and covers a lower side of the shift gears 122b-125b in the same manner as the second oil pool 114. The first end of the input shaft 120 is protruded toward an outside of the transmission case 103 through the end wall 103k and the second end of the input shaft 120 is protruded toward an inside of the final reduction chamber 101A through the dividing wall 102a. 
The final reduction gear unit 135 is mainly configured with a drive pinion 136 and a ring gear 137. The drive pinion 136 is provided at the second end of the intermediate shaft 121, which protrudes toward the inside of the final reduction chamber 101A, and the ring gear 137 is supported inside the final reduction gear unit case 102 and gear-meshes with the drive pinion 136 so that the ring gear 137 is freely rotatable about an axis line extending perpendicular to the intermediate shaft 121. A differential gear mechanism (not shown), provided at the ring gear 137, includes an output shaft 138 which projects in a width direction of the vehicle or perpendicularly to the sheet of FIG. 1 and coaxially with the ring gear 37 so as to drive vehicle wheels.
As can be seen from FIG. 8, an inlet opening 102b is formed at an upper part of the dividing wall 102a of the final reduction gear unit case 102, and a feedback opening 102c is formed at a lower part of the dividing wall 102a. The inlet opening 102b is positioned in an eccentric manner relative to the intermediate shaft 121 in the vicinity of a rotational surface of the ring gear 137. As can be seen from FIG. 9, three openings 103e-103g are vertically provided at the transmission chamber dividing wall 103c of the middle part case 103a. The openings 103e-103g are positioned in an eccentric manner relative to the intermediate shaft 121, to approximately correspond to the inlet opening 102b. Further, an opening 103h is also formed at the transmission chamber dividing wall 103c. The opening 103h is placed at an outer side of the flange portion 103d and is placed at a higher level than a bottom surface of the front part transmission chamber 101B2.
With the configuration of the above described conventional transmission apparatus, the lubricating oil stored at a lower part of the final reduction chamber 101A, i.e., the lowest part inside the casing 101, is lifted up by means of the ring gear 137 as indicated by an arrow F1 shown in FIG. 7 and the lubricating oil is supplied into the transmission chamber 101B through the inlet opening 102b of the dividing wall 102a as indicated by an arrow F6 shown in FIG. 7. Most part of the lubricating oil flows into the transmission chamber 101B then falls into the middle part transmission chamber 101B1, as indicated by an arrow F7 shown in FIG. 7, and the rest of the lubricating oil falls into the front part transmission chamber 101B2 through the openings 103e-103g, formed at the transmission chamber dividing wall 103c, as indicated by arrows F8 and F9 shown in FIG. 7. Accordingly, the lubricating oil lubricates meshing surfaces and sliding surfaces of the shift gears 22a-27a and 22b-27b and the selector sleeves 128-130. Further, the meshing surfaces and the sliding surfaces are also lubricated by means of the lubricating oil, which flows into the first and second oil pools 114 and 115 and is lifted up by means of the shift gears 122b-127b. 
Because the lubricating oil, stored at the lower part inside the final reduction chamber 101A, is lifted up by means of the ring gear 137, an oil level of the lubricating oil in the final reduction chamber 101A is lowered. Therefore, the lubricating oil in the middle part transmission chamber 101B1 is fed back to the final reduction chamber 101A through the feedback opening 102c as indicated by an arrow F5 shown in FIG. 7, and the lubricating oil in the front part transmission chamber 101B2 is fed back to the final reduction chamber 101A from the opening 3h, through the middle part transmission chamber 101B1, as indicated by an arrow F4 shown in FIG. 7. Accordingly, the lubricating oil is circulated among the final reduction chamber 101A, the middle part transmission chamber 101B1, and the front part transmission chamber 101B2. On this occasion, because the ring gear 137 is transmitted with the largest torque, a heat release value at the ring gear 137 is increased, and temperature of the lubricating oil in the final reduction chamber 101A is raised. The high-temperature lubricating oil is cooled by means of the transmission case 103 during lubrication in the middle part transmission chamber 101B1 and the front part transmission chamber 101B2, and then the lubricating oil is fed back to the final reduction gear unit case 102. Further, heat transmitted to the transmission case 103 from the high-temperature lubricating oil is discharged from an outer surface thereof and the transmission case 103 is thereby cooled.
However, with the configuration of such lifting-up type lubricating device, if the oil level of the lubricating oil in the chambers 101A, 101B1, and/or 101B2 fluctuate respectively due to vehicle driving conditions such as climbing and descending conditions, a longitudinal acceleration, a turning acceleration, or the like, there may be a lack of lubrication in a chamber in which the oil level of the lubricating oil is lowered. Thus, a possibility of causing an increase in abrasion of the meshing surface and the sliding surface or a seizure of the meshing surface and the sliding surface may occur. In view of the above mentioned considerations, the aforementioned transmission apparatus is provided with the opening 103h, formed at the transmission chamber dividing wall 103c, at the higher level than the bottom surface of the front part transmission chamber 101B2, for preventing a lowering of the oil level of the lubricating oil in the cambers 101A, 101B1, and/or 101B2 (especially in the front part transmission chamber 101B2) regardless of the climbing and descending conditions, the longitudinal acceleration, the turning acceleration, or the like, of the vehicle.
A method for evenly feeding the lubricating oil to the meshing surface and the sliding surface of the shift gears in the transmission case is disclosed in JP2000-240773A (see paragraphs [0037], and [0047]-[0048], and FIGS. 6 and 13). The transmission apparatus disclosed in JP2000-240773A includes a shower pipe, provided between an input shaft of shift gears, and an output shaft of shift gears, the shower pipe being parallel to the input and output shafts. Both ends of the shower pipe are supported by a casing and by a component fixed at the casing. Some of the lubricating oil discharged from an oil pressure pump is supplied to the shower pipe, and the lubricating oil is discharged from plural discharge openings provided at the side of the shower pipe to lubricate components (especially meshing portion of the gear) provided at the input and output shafts.
With the configuration of the conventional transmission apparatus illustrated in FIGS. 7-9, because the openings 103e-103g, formed at the transmission chamber dividing wall 103c, are required to avoid contact with boss portions or a reinforcing rib, which all support the shift gear shafts 120 and 121, a dimension and an arrangement of the openings 103e-103g are limited. Therefore, an amount of the lubricating oil, to be supplied into the front part transmission chamber 101B2 through the openings 103e-103g out of the lubricating oil which is lifted up from the lower part of the final reduction chamber 101A by means of the ring gear 137, and supplied into the transmission chamber 101B through the inlet opening 102b, may occasionally be insufficient. More specifically, the amount of the lubricating oil feeding into the front part transmission chamber 101B2 through the openings 103e-103g is decreased especially at the time of low speed driving, for example in a climbing condition. On this occasion, because the level of the lubricating oil in the front part transmission chamber 101B2 is lowered, an amount of the lubricating oil lifted up by means of the shift gears 22b-25b is decreased. In consequence, there is a lack of lubrication of the meshing surface and the sliding surface of the shift gears 22a-25a and 22b-25b and the selector sleeves 128 and 129, and the possibility of causing the increase of the abrasion of the meshing surface and the sliding surface or the seizure of the meshing surface and the sliding surface may increase. Further, in a condition where an amount of the lubricating oil supplied into the front part transmission chamber 101B2 is decreased, an amount of the lubricating oil circulating through the front part transmission chamber 101B2 is decreased, and heat discharged from the outer surface of the front part case 103b is decreased to some degree. Therefore, the temperature of the lubricating oil in the final reduction chamber 101A is raised. For reasons mentioned above, the lubricating oil is deteriorated, and an oil film of the meshing surface and the sliding surface lacks in a condition where a high-load engine torque is applied. In consequence, possibility of an early-stage abrasion or seizure of the meshing surface and the sliding surface may increase.
The above mentioned considerations may occur not only in a condition where the transmission chamber 101B is divided into the middle part transmission chamber 101B1 and the front part transmission chamber 101B2 as illustrated in FIGS. 7-9, but also in a condition where the transmission chamber 101B is a single chamber. More specifically, among from the total amount of the lubricating oil, which is lifted up from the lower part of the final reduction chamber 101A by the ring gear 137 and is supplied into the transmission chamber 101B, an amount of the lubricating oil, which can reach to a part placed far away from the ring gear 137, may be insufficient. Further, the amount of the lubricating oil supplied into the front part transmission chamber 101B2 through the openings 103e-103g is decreased especially at the time of low speed driving, for example in a condition of climbing. Therefore, the lubrication of the meshing surface and the sliding surface of the shift gears and the selector sleeves, the shift gears and the selector sleeves placed far away from the ring gear 137, lacks. In consequence, a possibility of causing the increase in the abrasion of the meshing surface and the sliding surface or the seizure of the meshing surface and the sliding surface may increase. Moreover, because the amount of the lubricating oil circulating through the part placed far away from the ring gear 137 is decreased, heat discharged from an outer surface of a part of the casing 101 placed far away from the ring gear 137 is decreased, and the temperature of the lubricating oil in the final reduction chamber 101A is raised. Thereby, the lubricating oil is deteriorated, and the oil film of the meshing surface and the sliding surface lacks in a condition where the high-load engine torque is applied. In consequence, a possibility of the early-stage abrasion or seizure of the meshing surface and the sliding surface may increase.
Fluctuation in an oil level of the lubricating oil in the chambers 101A, 101B1, and 101B2 due to the climbing and descending conditions, the longitudinal acceleration, or the like of the vehicle, in a condition where the transmission chamber 101B is divided into the middle part transmission chamber 101B1 and the front part transmission chamber 101B2, can be controlled to some extent by raising a position of the opening 103h of the transmission chamber dividing wall 103c. However, if the opening 103h is provided at a higher position, it may be possible that a good amount of the lubricating oil remains in the front part transmission chamber 101B2, at the time of a replacement of the lubricating oil in the casing 101. The aforementioned considerations may be avoided by providing an oil drain opening at a bottom portion of the front part transmission chamber 101B2, which can be opened and closed by means of a plug. However, a manufacturing cost, the number of components, and weight of the transmission apparatus may therefore increase. Further, some of the conventional transmission apparatuses of this type include plural openings 103j in the vicinity of a bottom surface of the transmission chamber dividing wall 103c as indicated by a chain double-dashed line shown in FIG. 9 for avoiding any possible inconvenience at the time of replacement of the lubricating oil. However, the transmission apparatus with the plural openings 103j cannot control a lowering of the lubricating oil in the front part transmission chamber 101B2.
According to the method, disclosed in JP2000-240773A, for evenly feeding the lubricating oil to the meshing surface and the sliding surface of the shift gears, the transmission apparatus requires the shower pipe, supporting members, for supporting the shower pipe to the casing, and the oil pressure pump, for feeding the lubricating oil. Therefore, the number of the components and weight of the transmission apparatus may increase.
The present invention has been made in view of the above circumstances, and provides a transmission apparatus which reliably supplies lubricating oil to a part placed far away from a rotational member without increasing a manufacturing cost, the number of components, weight, or the like.